Differences In Solution Chemistry Research Articles

INTERACTIONS BETWEEN ORGANIC AMENDMENTS AND PHOSPHATE FERTILIZERS MODIFY PHOSPHATE SORPTION PROCESSES IN AN ACID SOIL

To determine how organic amendments and phosphate fertilizers interact to modify P sorption processes, three phosphate fertilizers were applied to lignite- and compost-amended acid soil and incubated for either 3 or 26 days. The fertilizers applied were potassium dihydrogen phosphate, triple superphosphate, and diammonium phosphate (DAP). After 3 days of incubation, sorption of all three P sources was decreased in the lignite-amended treatments, whereas P sorption was increased in the compost-amended treatments. Increased incubation time (26 days) resulted in significantly decreased P sorption when DAP was added to lignite-amended treatments. Addition of triple superphosphate increased P sorption in lignite- and compost-amended treatments and decreased solution pH compared with DAP application. In addition to the effect of P source, differences in P sorption between the lignite- and compost-amended treatments were driven by differences in solution chemistry, predominantly solution pH and cation dynamics. Soil amendment and fertilizer addition also increased microbial activity in the incubation systems, as measured by carbon dioxide respiration. It is proposed that the combination of lignite and DAP may contribute to decreased P sorption in acid soils, with the positive effects likely caused by both chemical and biological processes, including the formation of soluble organic-metal complexes.

ORGANIC AMENDMENTS INCREASE SOIL SOLUTION PHOSPHATE CONCENTRATIONS IN AN ACID SOIL

Soil acidification affects at least 4 million hectares of agricultural land in Victoria, Australia. Low soil pH can inhibit plant growth through increased soluble aluminum (Al) concentrations and decreased available phosphorus (P). The addition of organic amendments may increase P availability through competition for P binding sites, solubilization of poorly soluble P pools, and increased solution pH. The effect of two organic amendments (lignite and compost) on P solubility in an acid soil was determined through controlled environment (incubation) studies. Three days after the addition of lignite and compost, both treatments increased orthophosphate and total P measured in soil solution, with the compost treatments having the greatest positive effect. Increased incubation time (26 days) increased soil solution P concentrations in both untreated and amended soils, with the greatest effect seen in total P concentrations. The measured differences in solution P concentrations between the lignite- and compost-amended treatments were likely caused by differences in solution chemistry, predominantly solution pH and cation dynamics. Soil amendment with lignite or compost also increased microbial activity in the incubation systems, as measured by carbon dioxide respiration. Based on the results presented, it is proposed that the measured increase in soil solution P with amendment addition was likely caused by both chemical and biological processes, including biotic and abiotic P solubilization reactions, and the formation of soluble organic-metal complexes.

Fate of DTPA, EDTA, and EDDS in Hydroponic Media and Effects on Plant Mineral Nutrition

ABSTRACT Synthetic chelators are commonly used in hydroponic media to solubilize iron (Fe); however, the fate of these chelators is unknown. This study examined the persistence of three synthetic chelators, ethylenediaminetetraacetate (EDTA), diethylenetriaminepentaacetate (DTPA), and ethylenediaminedisuccinate (EDDS) in a bench-scale lettuce production system. The EDDS concentration decreased rapidly within 7d, most likely due to biodegradation. The EDTA and DTPA concentrations stayed steady throughout the experiments despite additions to maintain a constant volume and loss of chelator may have been due to either plant uptake or photodegradation of the chelator. Despite large differences in solution chemistry, the final shoot concentrations of iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) were similar among chelator treatments, whereas root concentrations of these same elements were highly variable. The concentration of DTPA in a commercial lettuce production system was measured and highly variable concentrations were found.

Artifacts Caused by Collection of Soil Solution with Passive Capillary Samplers

Soil solution was collected with passive capillary samplers (PCAPS) and zero‐tension samplers (ZTS) from A horizons of forested soils. The volume and chemistry of collected solutions were measured weekly during discrete seasonal collection periods. Acid‐washed PCAPS increased alkalinity (3‐fold), pH (1–3 units), and concentrations of Ca (2‐fold), Na (8‐fold), and Si (4‐fold), relative to ZTS solutions. Aluminum concentrations were dramatically reduced in PCAPS compared with ZTS samples. Differences in solution chemistry were attributed to leaching and weathering of fiberglass wicking material utilized in the PCAPS. In addition, PCAPS collected greater volumes (normalized by sampler area) of solution relative to ZTS in weak‐structured sandy loam soil due to a preponderance of matrix flow. The results indicate that the PCAPS used in this study are not suitable for aqueous geochemical studies of dilute soil solutions.

Reversed calcite morphologies induced by microscopic growth kinetics: insight into biomineralization

This experimental investigation of calcite growth quantifies relationships between solution supersaturation and the rates of step advancement. Using in situ fluid cell atomic force microscopy (AFM), we show that the movement of monomolecular steps comprising growth hillocks on {1014} faces during the growth of this anisotropic material is specific to crystallographic direction. By quantifying the sensitivity of step growth kinetics to supersaturation, we can produce spiral hillocks with unique geometries. These forms are caused by a complex dependence of step migration rates, vs+ and vs−, upon small differences in solution chemistry as they grow normal to the conventional fast ([441]+ and [481]+) and slow ([441]− and [481]−) crystallographic directions. As solute activity, a, decreases, vs+ and vs− converge and growth hillocks express a pseudo-isotropic form. At still lower supersaturations where a approaches its equilibrium value, ae, an inversion in the rates of step advancement produces hillocks with unusual reversed geometries. Comparisons of the kinetic data with classical theoretical models suggest that the observed behavior may be due to minute impurities that impact the kinetics of growth through blocking and incorporation mechanisms. These findings demonstrate the control of crystallographic structure on the local-scale kinetics of growth to stabilize the formation of unusual hillock morphologies at the near-equilibrium conditions found in natural environments.

Physiological responses of plant leaves to atmospheric ammonia and ammonium

Misting of leaves of several plant species with 3 mM aqueous NH + 4 at pH 5, or fumigation with 3000 μg m -3 gaseous NH 3 for 1 h, elicits similar biochemical and physiological changes in the species tested. The enzyme glutamine synthetase (GS) was shown to increase its activity in all species, while that of nitrate reductase (NR) was inhibited, at least in those species which possessed the ability to induce foliar NR. At the same time there were marked changes in organic anion concentrations, with malate and citrate in particular being reduced in concentration, following either NH + 4 or NH 3 application to leaves. The changes in organic anions are also discussed in the light of pH regulation by the cell. A stimulation of photosynthesis was also evident when leaves were treated with either NH 3 or NH + 4. It is argued that, because of the differences in solution chemistry of the two ammonia forms, the aqueous form applied at pH 5 and the gaseous form being an alkali in solution, these changes can only have occurred through the ability of the leaves to readily assimilate both forms of the ammonia. The biochemical changes might have potential as markers for the onset of physiological perturbation by atmospheric ammonia pollution, particularly changes in organic acid concentration; their use in an index of pollution stress is briefly discussed.

A time series of vent fluid compositions from 21°N, East Pacific Rise (1979, 1981, 1985), and the Guaymas Basin, Gulf of California (1982, 1985)

A time series study of four hot spring fields at 21°N on the East Pacific Rise demonstrates that the solution compositions of mid‐ocean ridge hydrothermal vents are stable on a decadal time scale. The Ocean Bottom Seismometer (OBS), National Geographic Smoker (NGS), and South West (SW) vents show no significant changes in the major element composition of their end‐member fluids since 1979. Two of the vents, OBS and SW, have maintained exit temperatures near 350°C since 1979. The NGS vent has remained close to 270°C since 1981 after cooling from 350°C in 1979. Only one vent, Hanging Gardens, shows important changes in solution chemistry from 1981 to 1985. In 1985 this vent appears to have cooled ∼10°C relative to the other vents. The depth of the reaction zone, as determined by quartz geobarometry, has increased by about 1 km at this vent. The large fluxes of compositionally stable fluids from these vents cannot be explained by transient conditions and unique circumstances. Rather, the constancy of small interfield variations in solution composition is more consistent with control by rock buffering. A 4‐year time series study of hydrothermal vents in the Guaymas Basin also shows no significant changes in the major element composition of the end‐member fluids. Interfield differences in solution chemistry have been maintained from 1982 to 1985. This phenomenon is best explained in terms of an equilibrium model.

Mixed-Layer Kerolite/Stevensite from the Amargosa Desert, Nevada

AbstractMixed-layer clays composed of randomly interstratified kerolite/stevensite occur as lake and/or spring deposits of probable Pliocene and Pleistocene age in the Amargosa Desert of southern Nevada, U.S.A. The percentage of expandable layers of these clays, determined from computer-simulated X-ray diffractograms, ranges from almost 0 to about 80%. This range in expandabilities most likely results from differences in solution chemistry and/or temperature at the time of formation. An average structural formula for the purest clay (sample P-7), a clay with about 70% expandable layers, is: $${\left[ {\left( {M{g_{2,72}}A{l_{0,07}}F{e_{0.03}}L{i_{0.09}}} \right)\left( {S{i_{3.96}}A{l_{0.04}}} \right){O_{10}}{{\left( {OH} \right)}_2}} \right]^{ - 0.21}}{\left[ {X_{0.21}^ + } \right]^{ + 0.21}}.$$The data suggest that talc, kerolite, and stevensite form a continuous structural series based on layer charge.